The present invention relates to methods of coating substrates with a composition comprising a water continuous emulsion of a curable elastomeric polymer, and aqueous polyurethane dispersion, and an optional cure agent. Coated fabrics prepared according to these methods are particularly useful in the construction of automobile protective airbags.
The use of airbags in motor vehicles has grown exponentially in recent years. Their use has expanded beyond frontal airbags for protection for the driver and passenger. Side airbags and inflatable curtains are now included in side compartments of vehicles for enhanced protection from side collisions or rollovers. This expanded use has placed new demands on the physical properties attributed to the airbags. In particular, improved air retention performance of airbags are desired to ensure the airbag remains inflated and maintains its integrity for an extended period of time upon deployment.
Typically, airbags are made from synthetic fibers, such as a polyamide (nylon) or polyester and coated with a polymeric film. The most common polymeric materials currently being used to coat airbag fabrics are based on silicones, as described for example in U.S. Pat. No. 6,037,279. The silicone coating primarily provides a thermal barrier on the airbags to protect the fabric from the high temperature burst associated with ignition of the gas upon deployment. The silicone coating also provides some gas retention properties for the deployed airbag. One option to meet the increasing demand for gas retention is to increase the thickness of the silicone coating. However, newer designs for airbags, and in particular side impact airbags and inflatable curtains for side compartments, require airbags to have a more compact design. This results in a need for lower coating weights on the airbag fabrics. Furthermore, next generation side and inflatable curtain airbags have a need to retain pressured air/gas for sufficient time to provide rollover protection for greater than 5 seconds. Current silicone based coatings are too permeable to air/gas, especially at lower coat weights, to provide sufficient gas retention in deployed side and curtain airbags. Thus, there is a need for a fabric coating composition, and methods of application, to provide coated fabrics with sufficient air/gas retention for use in the construction of airbags, and in particular side and curtain airbags.
The current airbag fabrics also requires the removal of unwanted sizing, protective oil after woven steps before application of the coating material. This is done by chemical scouring, washing, then drying of the scoured airbag fabrics. These steps are non-value added, labor-intensive, and costly. Also, residual moisture on the fabric surface can cause imperfections on the coated surface when a non-aqueous coating is applied. Thus, there exsits an additional need to develop a coating composition that can be applied directly over wet fabrics, provides good adhesion to the fabric, and dries to a uniform coating without imprefections.
One technique that has been reported to decrease coating weights and maintain low permeability performance of coated fabrics for use in airbags has been to use a two layered coating system, as disclosed for example in U.S. Pat. No. 6,177,365. The U.S. Pat. No. 6,177,365 patent teaches the application of a first layer to the fabric of a non-silicone material followed by the application of a silicone containing topcoat. U.S. Pat. No. 6,177,366 also teaches a two layer coating system for airbag fabrics where the first layer contains up to 30% of a silicone resin and the topcoat contains a silicone material. U.S. Pat. No. 6,239,046 teaches an airbags having a first coating layer of adhesive polyurethane and a second coating layer of an elastomeric polysiloxane.
Alternative coating compositions have been disclosed based on polyurethanes, such as in U.S. Pat. No. 5,110,666, or on polyurethane/polyacrylate dispersions as found in U.S. Pat. No. 6,169,043.
While the coating systems cited above represents advancements in airbag technology, a need still exists to provide improved compositions and techniques for coating fabrics for use in airbags. In particular, coating compositions that provide similar or improved permeability at lower coating weights and improved aging stability are desired. Furthermore, there is a need to provide coatings that eliminate the need for pre-treatment of the fabrics.
The present invention is directed to a method for coating a substrate comprising the steps of:
(I) applying a layer on the substrate of a curable composition comprising:
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C.,
(B) an aqueous polyurethane dispersion, and optionally
(C) a cure agent
(II) exposing the layer to air for sufficient time to form a cured coating. The present invention further provides a method for forming a cured second coating of a composition comprising a polyorganosiloxane-based elastomeric material upon the first cured coating.
The present invention is also directed to the coated substrates prepared by the methods described herein.
Step (I) of the method of the present invention is applying a layer on a substrate of a curable composition comprising:
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C.,
(B) an aqueous polyurethane dispersion, and optionally
(C) a cure agent
Component (A) is a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C. As used herein, xe2x80x9cwater-continuous emulsionxe2x80x9d refers to an emulsion having water as the continuous phase of the emulsion. Water-continuous emulsions are characterized by their miscibility with water and/or their ability to be diluted by the further addition of water.
The elastomeric polymers that can be used as starting materials to prepare the water continuous emulsion suitable as component (A) in the present invention, are any polymers having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C. One skilled in the art recognizes the term elastomeric to describe materials as having rubber-like properties or rubbery characteristics, that is, materials which can be extended to twice its own length at room temperature or having an elongation of 100% or higher at room temperature. When the term xe2x80x9cpolymerxe2x80x9d is used herein, it should be understood to describe polymers that may be homopolymers, copolymers, terpolymers, and mixtures thereof.
For the purpose of this invention, the viscosity of the curable elastomeric polymer is defined as xe2x80x9czero-shearxe2x80x9d viscosity at ambient temperature. This is commonly defined as the viscosity of a polymer when approaching zero-shear rate conditions and is regarded as a constant value for a given polymer. The xe2x80x9czero-shearxe2x80x9d viscosity is an approximated constant viscosity value derived empirically or from experimentally measured viscosity values.
The curable elastomeric polymers suitable in the present invention can have a viscosity of 0.5 to 1,000,000 KPa-s, preferably the viscosity is 0.5 to 500,000 KPa-s, and most preferable is when the curable elastomeric polymer has a viscosity of 1.0 to 100,000 KPa-s. While the correlation of viscosity and molecular weight will vary depending on the specific type of polymer, generally the number average molecular weights (Mn) of the curable elastomeric polymers that can be typically used in the present invention range from 5,000 to 300,000 g/mole, preferably 5,000 to 200,000 g/mole, and most preferably range from 5,000 to 100,000 g/mole.
For purposes of this invention, the term xe2x80x9cglass transition temperaturexe2x80x9d is the accepted meaning in the art, that is, the temperature at which a polymer changes from a brittle vitreous state to a plastic state. The glass transition temperature can be determined by conventional methods such as dynamic mechanical analyzer (DMA) and differential scanning calorimetry (DSC). The curable elastomeric polymers of the present invention should have a glass transition temperature of less than 50xc2x0 C. Preferably, the curable elastomeric polymers of the present invention should have a glass transition temperature of less than 30xc2x0 C., and more preferably, the curable elastomeric polymers should have a glass transition temperature of less than 0xc2x0 C.
As used herein, xe2x80x9ccurable elastomeric polymerxe2x80x9d refers to any elastomeric polymer that has been modified to have at least one curable functional group attached to the polymer. Generally, curable elastomeric polymers are polymers having reactive groups contained therein that are able to crosslink during the curing process to yield an elastomeric polymer. The curable elastomeric polymers can be characterized as elastomeric polymers to which at least one reactive group or functional group is attached such as an alkenyl, vinyl, allyl, hydroxyl, carboxyl, epoxy, vinyl ether, alkoxy, amine, amino, amido, silane, organosilane, or organosilyl group. The reactive-group or functional group may be attached at a terminal and/or pendant position on the polymer chain. The curable elastomeric polymer should maintain structural integrity during the emulsification process and subsequently in the emulsion state. Upon water-removal, for example as in a coating application, the reactive-group or functional group cures to form a cured elastomeric polymer. The curing may take place by merely drying off the water, or assisted by an external catalyst, heat, radiation, moisture, or in conjunction with an external curative.
The elastomeric polymers that can be used as starting materials to prepare the curable elastomeric polymers and subsequently emulsified to form water continuous emulsions suitable as component (A) of the present invention include, but are not limited to, the elastomeric polymers typically associated with the following general classes of elastomeric materials such as; natural rubber, polyolefins, poly(olefin-diene)s, polydienes, butyl rubber, nitrile rubber, chloroprene rubber, fluorocarbon elastomers, polysulfide rubbers, polyurethane and combinations thereof.
Illustrative examples of elastomeric polymers that can be functionalized to produce curable elastomeric polymers useful in the preparation of water continuous emulsions for the present invention include, but are not limited to: poly(olefins) and poly(olefins-dienes) copolymers, and their derivatives, that is, polymers and copolymers derived from olefinic monomers C2 to C12, dienes C4 to C12 such as, polyethylene, polypropylene, poly(butene-1), poly(propylethylene), poly(decylethylene), poly(dodecylethylene), poly(butylethylene), poly(ethylethylene), poly(ethyl-2-propylene), poly(isopropylethylene), poly(isobutylethylene), poly(isopentylethylene), poly(heptylethylene), poly(tert-butylethylene), poly(ethyele-co-propylene), poly(ethylene-propylene-diene) terpolymers (EPDM); polymers and copolymers of monoolefin, isomonoolefin and vinyl aromatic monomers, such as C2 to C12 monoolefins, C4 to C12 isomonoolefins, vinyl aromatic monomers including styrene, para-alkylstyrene, para-methylstyrene, (methods of preparing such polymers can be found in U.S. Pat. No. 5,162,445, and U.S. Pat. No. 5,543,484); poly(dienes) and derivatives; such as, polybutadiene, polyisoprene, poly(alkyl-butenylene) where alkyl can be a hydrocarbon group containing 1 to 12 carbon atoms, poly(phenyl-butenylene), polypentenylene, natural rubber (a form of polyisoprene), butyl rubber (copolymer of isobutylene and isoprene), illustrative commercial examples of polyisobutylenes suitable in the present invention are OPPANOL B products from BASF (BASF, Ludwigshafen, Germany), VISTANEX(trademark) products from Exxon (Houston, Tex.), and EPION products from Kaneka (Kanegafuchi Chemical Industry Co. Ltd. Tokyo, Japan and Kaneka America Corp, New York, N.Y.); halogenated olefin polymers; such as from the bromination of copolymers of isomonoolefin with para-methylstyrene to introduce benzylic halogen (as described in U.S. Pat. No. 5,162,445), halogenated polybutadienes, halogenated polyisobutylene such as EXXPRO(trademark) products from Exxon-Mobil (Houston, Tex.), poly(2-chloro-1,3-butadiene), polychloroprene (85% trans), poly(1-chloro-1-butenylene) (NEOPRENE(trademark)), chlorosulfonated polyethylene; polyurethanes and polyureas; such as elastomeric polyurethanes and polyureas prepared from a wide variety of monomeric diisocyanates (aliphatic diisocyanates such as hexamethylene diisocyanate, cyclohexyldiisocyanate, (H12MDI) or hydrogenated MDI (HMDI), isophorone diisocyanate (IPDI)); aromatic diisocyanates such as toluene diisocyanate (TDI), bis(methylene-p-phenyl diisocyanate (MDI), chain-extending diols, diamines, and oligomeric diols selected from polyether, polyester, polycarbonate, and polycaprolatom; poly(alkyl acrylates), and poly (alkyl methacryaltes), that is polymers and copolymers derived from alkyl acrylates and alkyl methacrylates such as poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate), poly(isobutyl acrylate), poly(2-ethylbutyl acrylate), poly(2-ethylhexyl acrylate), poly(n-octyl methacrylate), poly(dodecyl acrylate); copolymers and terpolymers of dienes, alkenes, styrenes, acrylonitriles, such as poly(butadiene-co-styrene), poly(butadiene-co-acrylonitrile), poly(butadiene-co-methyl metharyalte); poly(fluoroalkyl acrylates) that is polymers and copolymers derived from fluoro-containing acrylates and methacrylates such as polymer(fluoromethyl acrylate), poly(2,2,2-trifuoroethyl acryalte), poly(1H,1H-pentfluoropropyl acryate), poly(1H,1H,5H-octafluoropentyl acrylate); poly(vinyl ethers) and poly(vinyl thioethers) such as those polymers derived from butoxyethylene, sec-butoxyethylene, tert-butoxyethylene, alkyl vinyl ether, propoxyethylene, vinyl methyl ether (methoxyethylene), hexyloxyethylene, 2-ethylhexyloxy ethylene, butylthioethylene; poly(oxyalkylenes) such as poly(oxyethylene), poly(oxypropylene), poly(oxythylene-co-propylene); plasticizer compounded thermoplastics, that is thermoplastics having elastomeric behavior because of the addition of a plasticizers or other compatible additives, such as poly(vinyl chloride) compounded with dioctyl phthalate, tricresyl phophate, dibutyl sebacate, or poly(propylene adipate); fluoro elastomers and chloro-containing polymers derived from poly(alkylenes), poly(dienes) such as, poly(dichloroethyelene), poly(chlorofluoroethylene).
Thus, the curable elastomeric polymer can be an alkenyl-functional elastomeric polymer where the alkenyl group is selected from a hydrocarbon group containing 2 to 12 carbons such as vinyl, allyl, propenyl, butenyl, hexenyl, etc. The elastomeric polymers bearing such alkenyl functional groups may be derived from most of the elastomeric polymers, as described above, including poly(olefins) and poly(olefins-dienes) copolymers, and their derivatives: polymers and copolymers derived from olefinic monomers C2 to C12, dienes C4 to C12; polymers and copolymers of monoolefin, isomonoolefin and vinyl aromatic monomers: monoolefin C2 to C12, isomonoolefin C4 to C12, vinyl aromatic monomers including styrene, para-alkylstyrene, para-methylstyrene; examples include polymers derived from ethylene, propylene, isobutylene, isoprene, para-methylstyrene.
The curable elastomeric polymers can also be poly(dienes) and derivatives. Most of polymers, copolymers derived from dienes usually contain unsaturated ethylenic units on backbone or side-chains that are curable. Representative examples include polybutadiene, polyisoprene, polybutenylene, poly(alkyl-butenylene) where alkyl being C1 to C12, poly(phenyl-butenylene), polypentenylene, natural rubber (a form of polyisoprene); butyl rubber (copolymer of isobutylene and isoprene).
The curable elastomeric polymers can also be a halogenated olefin polymer. Representative examples of a halogenated olefin polymer include those polymers resulting from the bromination of a copolymer of isomonoolefin with para-methylstyrene to introduce benzylic halogen (as described in U.S. Pat. No. 5,162,445), halogenated polybutadienes, halogenated polyisobutylene, poly(2-chloro-1,3-butadiene), polychloroprene (85% trans), poly(1-chloro-1-butenylene) (NEOPRENE(trademark)), chlorosulfonated polyethylene. The brominated poly(isobutylene-co-para-methylstyrene) can be further cured via zinc oxide upon influence of heat.
The curable elastomeric polymers can also be polymers containing vinyl ether-, acrylate-, methyacrylate-, and epoxy-functional groups. Also, the elastomeric polymers can be hydroxyl terminal or hydroxy containing poly(oxyalkylenes) polymers, such as poly(oxyethylene), poly(oxypropylene), or poly(oxythylene-co-propylene) polymers.
The curable elastomeric polymer can be selected from reactive silane group-containing elastomeric polymers, mixtures of reactive silane group-containing elastomeric polymers, blends of reactive silane group-containing elastomeric polymers with conventional elastomeric polymers, mixtures or blends of conventional elastomeric polymers with reactive silane group containing silicone polymers. The reactive silane groups may be attached at the terminal and/or pendant positions on the polymer chain and the total number of these reactive silicone groups may be varied to provide a cured elastomeric structure with desirable properties. Representative silane-modified elastomeric polymers are silyated polymers and copolymers derived from olefins, such as the isobutylene polymers disclosed in U.S. Pat. No. 4,904,732, which is hereby incorporated by reference, isomonoolefin, dienes, ethylene or propylene oxides, vinyl aromatic monomers from C2 to C12 such as the silane-grafted copolymers of isomonoolefin and vinyl aromatic monomer as discussed in U.S. Pat. Nos. 6,177,519 B1 and 5,426,167. Commerical products illustrative of silylated propylene oxide polymers are the MS Polymers from Kaneka (Kanegafuchi Chemical Industry Co. Ltd. Tokyo, Japan and Kaneka America Corp, New York, N.Y.). Other representative silicon-modified elastomeric polymers are illustrated by, but not limited to; alkenylsilyl-functional elastomeric polymers such as vinylsilyl-, allylsilyl-, hexenylsilyl-containing elastomeric polymers that are curable to form and further the elastomeric polymer structure; and alkoxysilyl-functional elastomeric polymers such as polymers containing at least one alkoxylsilyl groups and/or their hydrolysates selected from methoxysilyl, dimethoxysilyl, trimethoxysilyl, ethoxysilyl, diethoxysilyl, triethoxysilyl, and methoxyethoxylsilyl.
In one embodiment of the present invention, the curable elastomeric polymer is selected from the silylated copolymers of an isomonoolefin and a vinyl aromatic monomer as described in U.S. Pat. No. 6,177,519 B1, which is hereby incorporated by reference. The silylated copolymers may be characterized as the addition product of an olefin copolymer radical created by contact of the copolymer with a free radical generating agent and an olefinically unsaturated, hydrolyzable silane wherein the silane adds to the polymer backbone to produce a silane grafted or silane modified copolymer product.
Illustrative examples of olefin copolymers suitable for modification with silanes to produce the silylated copolymers of this embodiment of the present invention comprise copolymers containing at least 50 mole % of at least one C4 to C7 isomonoolefin and from 0.1 up to 50 mole % of at least one vinyl aromatic monomer. Typically, the vinyl aromatic monomers are mono-vinyl aromatics such as styrene, alpha-methylstyrene, alkyl-substituted styrenes such as t-butylstyrene and para-alkyl substituted styrenes wherein the alkyl group contains from 1 to 4 carbon atoms, more preferably para-methylstyrene. Suitable isomonoolefin monomers include isobutylene and the like. Typically, 100% of the isomonoolefinic content of the copolymer comprises isobutylene. Typically, olefin copolymers include elastomeric copolymers comprising isobutylene and para-methylstyrene and containing from about 0.1 to 20 mole % of para-methylstyrene. These copolymers have a substantially homogeneous compositional distribution such that at least 95% by weight of the polymer has a para-methylstyrene content within 10% of the average para-methylstyrene content of the polymer. They are also characterized by a narrow molecular weight distribution Mw/Mn (where Mw is weight average molecular weight, and Mn is number average molecular weight) of less than about 5, alternatively less than about 3.5, a glass transition temperature (Tg) of below about xe2x88x9250xc2x0 C. and a number average molecular weight (Mn) in the range of about 2,000 to 1,000,000, and alternatively from 10,000 to 50,000.
Suitable unsaturated organic silanes which can be reacted with the olefin copolymer backbone to produce the silylated copolymers of this embodiment are of the general formula RRxe2x80x2SiY2 wherein R represents a monovalent olefinically unsaturated hydrocarbon or hydrocarbonoxy radical reactive with the free radical sites produced on the backbone polymer, Y represents a hydrolyzable organic radical and Rxe2x80x2 represents an alkyl or aryl radical or a Y radical. Where R is a hydrocarbonoxy radical, it should be non-hydrolyzable. In the preferred embodiment R may be a vinyl, allyl, butenyl, 4-pentenyl, 5-hexenyl, cyclohexenyl or cyclopentadienyl radical, with vinyl being the preferred radical. The group Y may be one or a mixture of C1 to C4 alkoxy radical such as methoxy, ethoxy, propoxy, or butoxy; Y may also be selected from acyloxy radicals such as formyloxy, acetoxy or propionoxy; oximo radicals such as xe2x80x94ONxe2x95x90C(CH3)2, xe2x80x94ONxe2x95x90C(CH3)(C2H5) and xe2x80x94ONxe2x95x90C(C6H5)2; or substituted amino radicals such as alkylamino or arylamino radicals, including xe2x80x94NHCH3, xe2x80x94NHC2H5 and xe2x80x94NHC6H5 radicals. The group Rxe2x80x2 represents either an alkyl group, an aryl group or a Y group. The group Rxe2x80x2 can be exemplified by a methyl, ethyl, propyl, butyl, phenyl, alkylphenyl group or a Y group. Alternatively, Rxe2x80x2 is a methyl or alkoxy group. Typically, the silanes are those where Rxe2x80x2 and Y are selected from methyl and alkoxy groups, e.g., vinyltriethoxysilane, vinyltrimethoxysilane and methyl vinyl dimethoxysilane.
Typically, the free radical initiator used to create the silylated copolymers for this embodiment of the present invention is an organic peroxide compound having a half-life, at the reaction temperature, of less than one tenth of the reaction/residence time employed.
The water continuous emulsions comprising a curable elastomeric polymer can be selected from the emulsions described in U.S. application Ser. No. 09/905,660, which is hereby incorporated by reference. U.S. application Ser. No. 09/905,660 describes water-continuous emulsion composition comprising;
(A) 100 parts of a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C.,
(B) 3 to 30 parts surfactant
(C) 0.5 to 50 parts of an internal cure additive
(D) 5 to 45 parts water
wherein the water-continuous emulsion has a solids content of greater than 75 weight %, an average particle size less than 5 xcexcm, having sufficient stability to produce a stable lower solids emulsion upon dilution with water.
Component (B) of the compositions of the present invention is a polyurethane dispersion. xe2x80x9cPolyurethane dispersionxe2x80x9d as used herein describes stable mixtures of polyurethane polymers in water. Methods of preparing polyurethane dispersions are well known in the art and many of polyurethane dispersions are commercially available. Polyurethane polymers are generally characterized by their monomer content and most commonly involve the reaction of a diisocyanate with a polyol and chain extender. While the present inventors believe the polyurethane dispersion can be a stable aqueous mixture of any known polyurethane, typically the polyurethanes suitable for the use in the aqueous polyurethane dispersions are the reaction products (a) an isocyanate compound having at least two isocyanate (xe2x80x94NCO) functionalities per molecule; (b) a polyol having at least two hydroxy functionalities per molecule and a molecular weight ranging from 250 to 10,000 g/mole. The polyol may be selected from those commonly found in polyurethane manufacturing such as hydroxy-containing or terminated polyethers, polyesters, polycarbonates, polycaprolactones, polythioethers, polyetheresters, polyolefins, and polydienes. Suitable polyether polyols for the preparation of polyether polyurethanes and their dispersions include the polymerization products of cyclic oxides such as ethylene oxide, propylene oxide, tetrahydrofuran, or mixtures thereof. Polyether polyols commonly found include polyoxyethylene (PEO) polyols, plyoxypropylene (PPO) polyols, polyoxytetramethylene (PTMO) polyols, and polyols derived from the mixture of cyclic oxides such as poly(oxyethylene-co-polypropylene) polyols. Typical molecular weight of polyether polyols can range from 250 to 10,000 g/mole. Suitable polyester polyols for the preparation of polyester polyurethanes and their aqueous dispersions include; hydroxy-terminated or containing reaction products of ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1-4, butanediol, furan dimethanol, polyether diols, or mixtures thereof, with dicarboxylic acids or their ester-forming derivatives.
Modified polyether polyurethanes such as polyetherester polyurethanes and polyethercarbonate polyurethanes may also be suitable polyurethanes for the preparation of aqueous polyurethane dispersions. These modified polyether polyurethanes can be derived by incorporating additional polyester polyols or polycarbonate polyols into polyether polyols during the polyurethane manufacturing.
Typically the polyurethane polymer useful to prepare the polyurethane dispersion as component (B) in the compositions of the present invention is selected from polyether polyurethanes, polyester polyurethanes, polycarbonate polyurethanes, polyetherester polyurethanes, polyethercarbonate polyurethanes, polycaprolactone polyurethanes, hydrocarbon polyurethanes, aliphatic polyurethanes, aromatic polyurethanes, and combinations thereof.
xe2x80x9cPolyurethane dispersionxe2x80x9d as used herein encompasses both conventional emulsions of polyurethane polymers, for example where a preformed polyurethane polymer is emulsified into an aqueous medium with the addition of surfactants and application of shear, and also includes stable mixtures of self-dispersing polyurethane polymers. Polyurethane dispersions of self-dispersing polyurethane polymers are well known in the art and many are commercially available. These polyurethane dispersions are generally free of external surfactants because chemical moieties having surfactant like characteristics have been incorporated into the polyurethane polymer and therefore are xe2x80x9cself emulsifyingxe2x80x9d or xe2x80x9cself dispersingxe2x80x9d. Representative examples of internal emulsifier moieties that can be incorporated into the polyurethane dispersions useful in the present invention include; ionic groups such as sulfontates, carboxylates, and quaternary amines; as well as nonionic emulsifier groups such as polyethers. Such polyurethane dispersions are well known in the art, and are typically prepared by either a one stage or two-stage process. Typically, a isocyanate-terminated polyurethane prepolymer is made from isocyanates, polyols, optional chain extender, and at least one monomer containing a hydrophilic group to render the prepolymer water dispersible. The polyurethane dispersion can then be prepared by dispersing the isocyanate-terminated polyurethane prepolymer in water with other polyisocyanates. Further chain extension can be affected by the addition of chain extenders to the aqueous dispersion. Depending on the choice of the hydrophilic group used to render the polyurethane polymer water dispersible, an additional reaction step may be needed to convert the hydrophilic group to an ionic species, for example converting a carboxyl group to an ionic salt or an amine to an amine salt or cationic quaternary group.
Representative, non-limiting examples of polyurethane dispersions that are suitable for use as component (B) in the compositions of the present invention, as well as general descriptions of techniques useful to prepare polyurethane dispersions can be found in U.S. Pat. Nos. 4,829,122, 4,921,842, 5,025,064, 5,055,516, 5,308,914, 5,334,690, 5,342,915, 5,717,024 5,733,967, 6,017,998, 6,077,611, 6,147,155, and 6,239,213.
Representative, non-limiting examples of commercially available polyurethane dispersions that are suitable for use as component (B) in the compositions of the present invention include: WITCOBOND W 290H, W-290H, W-296, and W213 (Uniroyal Chemical Division, Crompton Corporation, Middlebury, Conn.); DISPERCOLL U42, BAYHYDROL 121, and Bayhydrol 123 polycarbonate polyurethane dispersions (100 Bayer Road, Pittsburgh, Pa. 15025); SANCURE 2710 and 2715 aliphatic polyether polyurethane dispersions (Noveon, Inc. Cleveland, Ohio); NEOREZ R-966, R-967, R-9603 aliphatic polyurethane dispersions (NeoResins Division, Avecia, Wilmington, Mass.).
Optional component (C) is a cure agent. As used herein, a cure agent is any component added to the compositions of the present invention that enhances the curing of the coatings therefrom. One skilled in the art would be able to select an appropriate cure agent given the type of curable groups present on the curable elastomer polymer used in the water continuous emulsion of component (A). Generally, suitable curing agents are water dispersable materials selected from epoxies, silanes, polyaziridines, carbodimide, isocyanates, polyisocyanates, cyanurates, melamines and combinations thereof.
The amount of component (C) used is an amount to effectively cause curing of the coating compositions and will also vary depending on the type of curable groups present on the curable elastomeric polymer.
Representative, but non-limiting examples of typical cure agents useful in the present invention include: WITCOBOND XW from Crompton Corporation (CK Witco Corporation, Middlebury, Conn.); water-reducible melamine resins such as CYMEL 370, CYMEL 373 from CYTEC Industries Inc. (West Paterson, N.J.); polyfunctional aziridines such as IONAC XAMA-7, XAMA-220 from Sybron Chemicals Inc. (Birmingham, N.J.); water-reducible epoxy resins such as EPI-REZ Resin WD-510, and waterborne epoxy resins such as EPI-REZ 3522-W-60, both from Resolution Performance Products (Huston, Tex.; previously Shell Chemical Co.); silanes for aqueous cross-linking of the emulsion coatings include DOW CORNING 777 siliconate and 1-6634 aminopropyl siliconate (Dow Coming Corporation, Midland, Mich.).
Other additives can be optionally incorporated into the curable coating composition of this invention, as component (D), to derive additional specific features. Such additives include, but not limited to; reinforcing or extending fillers such as colloidal silica, fumed silica; colorants and pigments; stabilizers as thermal, UV, and weathering stabilizers; flame retardants, thickeners, biocides, and preservatives.
The curable emulsion coating composition typical of the present invention is a water-continous emulsion emulsion having a non-volatile solids content between 5% to 80% by weight. The non-volatile portion of the coating composition comprises the curable elastomeric polymer of component (A) from 5 to 60 parts, and the polyurethane polymer of component (B) from 40 to 95 parts, and the total solids of components (A) and (B) being 100 parts by weight. Alternatively, the component (A) is present from 10 to 50 parts and the component (B) from 50 to 90 parts; alternatively, the component (A) ranges from 20 to 50, and the component (B) ranges from 50 to 80 parts by weight. The curing agent (C) can be incoporated up to 10 parts, and the reinforcing additive component (D) can be present up to 40 parts, based on a 100 parts total of (A) and (B) components.
The curable coating compositions can be prepared by mixing components (A), (B), and optionally (C) and (D) by any of the techniques known in the art such as milling, blending, and stirring, either in a batch or continuous process. The technique and particular device selected is determined by the viscosity of the components and final curable coating composition. The curable coating compositions can be prepared by one of two mixing procedures, depending on the type of polyurethane dispersion, and the relative ratio of curable elastomers in component (A) to the polyurethane polymer in component (B). When preparing a coating composition comprising an acid curable emulsion of an elastomer such as a silylated poly(isobutylene) (abbreviated SiPIB) and polyurethane dispersions of pH 7.0 or higher (i.e. neutral or anionic types of polyurethane dispersion), the pH can be first adjusted to raise the pH of the curable SiPIB emulsion with an alkaline additive such as colloidal silica (or alternatively, a base compound such as 2-amino-2-methyl-1-propanol, AMP) to 6.0 or higher, prior to incorporating the selected polyurethane dispersions. In these types of coating compositions, the pH should be maintained at a value of 6.0 or above, to ensure stability and compatibility. The final pH of the mixture disclosed in this invention varies, depending upon the choice of polyurethane dispersion.
The other method of coating preparation relates to the coating compositions comprising an acidic curable elastomeric emulsion and an acidic polyurethane dispersion. In such cases, the final coating mixtures are acidic and no pH adjustment is needed, as the individual components and finished coating are all acidic and compatible.
The curable coating composition can also be prepared by adding the mixture of components (B), (C), and (D) into component (A) through a dynamic or static mixer to result in a uniform coating composition. This method is particularly desirable in a continuous operation, provided sufficient shear and mixing time can be realized.
The curable compositions can be applied to a variety of substrates, such as fabrics, fibers, yarns, textiles and films according to known techniques. These techniques include, but not limited to, knife coating, roll coating, dip coating, flow coating, squeeze coating, and spray coating. Knife coating includes knife-over-air, knife-over-roll, knife-over-foam, and knife-over-gap table methods. Roll coating includes single-roll, double-roll, multi-roll, reverse roll, gravure roll, transfer-roll coating methods.
The curable compositions can also be applied to wet fabrics, immediately following a scouring operation. The compositions provide good adhesion to the fabric surface, and dries to a uniform coating without imperfections.
Step (II) of the method of the present invention is exposing the layer of the curable composition on the substrate to air for sufficient time to form a cured coating. Step (II) can be accelerated by increasing the temperature at which this step is performed, for example, from about room temperature to about 180xc2x0 C., alternatively from room temperature to about 150xc2x0 C., or alternatively from about room temperature to about 130xc2x0 C., and allowing the coating to cure for a suitable length of time. For example, the coating composition typically cures in less than about 3 min at 150xc2x0 C.
An alternative embodiment of the present invention provides a method for coating a substrate comprising the steps of:
(I) applying a first layer on the substrate of a curable composition comprising;
(A) a water continuous emulsion comprising a curable elastomeric polymer having a viscosity of 0.5-1,000,000 KPa-s and a glass transition temperature up to 50xc2x0 C.,
(B) an aqueous polyurethane dispersion, and optionally
(C) a cure agent,
(II) exposing the first layer to air for sufficient time to form a cured first coating,
(III) applying a second layer on the cured first coating of a composition comprising a polyorganosiloxane-based elastomeric material,
(IV) exposing the second layer to air for sufficient time to form a cured second coating.
In this alternative embodiment, steps (I) and (II) are the same as described previously. Step (III) is applying a second layer on the cured first coating of a composition comprising a polyorganosiloxane-based elastomeric material. The polyorganosiloxane-based elastomeric material can be any silicone based material known in the art for coating substrates, and in particular, fabric or textile substrates. Alternatively, polyorganosiloxane-based elastomeric material can be chosen from the class of silicones known in the art as liquid silicone rubber. Alternatively, the polyorganosiloxane-based elastomeric materials which may be useful as a second layer in Step (III) are described for example in U.S. Pat. No. 6,037,279, which is hereby incorporated by reference. The techniques for applying the second layer can be the same as those described previously for Step (I). Step (IV) is exposing the second layer to air for sufficient time to form a cured second coating. The techniques for exposing the second layer to air for sufficient time to form a cured second coating can be the same as those described for Step (II) above. In a similar manner, Step (IV) can be accelerated by increasing the temperature at which this step is performed, for example, from about room temperature to about 180xc2x0 C., alternatively from room temperature to about 150xc2x0 C., or alternatively from about room temperature to about 130xc2x0 C., and allowing the coating to cure for a suitable length of time. For example, the coating composition typically cures in less than about 3 min at 150xc2x0 C.
Substrates can be coated with various amounts of the compositions described above and cured. The coat weight, or coating weight, as used herein describes the net amount of dried coating material deposited onto a substrate. The coating weight on a given substrate or fabric is the difference between the gross weight of a dried coated substrate or fabric and the weight of a dried substrate or fabric having a same dimension. The method for determining the coated and uncoated fabric is similar to ASTM D3776. Typical coating weight ranges for the coatings of the present invention are 10 to 120 g/m2 (gsm) (or 0.28 to 3.4 ounces/square yard), alternatively, the range for the coating weight is 10 to 80 g/m2 (or 0.28 to 2.28 ounces/square yard), or alternatively the coating weight is 10 to 60 g/m2 (or 0.42 to 1.7 ounces/square yard). When a two-coat system is used, as described above in the alternative embodiment, the coating weight range for the second coating is 5 to 50 g/m2 (or 0.14 to 1.43 ounces/square yard); alternatively the second coating range is 5 to 30 g/m2 (or 0.14 to 0.86 ounces/square yard); or alternatively is 10 to 20 g/m2 (or 0.28 to 0.57 ounces/square yard).
Coated substrates prepared according to the methods of the present invention have excellent mechanical properties resulting from the cured coatings on the substrate. Furthermore, the methods of the present invention provide coated substrates with improved air/gas retention properties at relatively low coating weights which make them useful in the manufacture of airbag and inflatable curtains that require long hold-up time during deployment.